I'm not sure if this goes in the digital or analog section, so please forgive me if I chose poorly.

I have an FPGA that is an HDMI source. The design is working fine while everything is powered on. However, when I power down the FPGA board with the monitor still powered, the pull-up resistors in the TMDS sink (the monitor) back-drive into the FPGA and cause it to go into a quasi-powered state.

Apparently this is not uncommon, and there are buffer ICs and such. So I'm looking into a few options and I have found a chip that looks like what I need, the TPD12S016 (http://www.ti.com/lit/ds/symlink/tpd12s016.pdf)

The datasheet says it provides "Back-drive Protection on HDMI Connector Side Ports", "ESD protection", etc. What is unclear to me is if the back-drive "protection" is for the device itself, i.e. meaning the TPD12S016 will not provide a path for back-drive currents, or it the device is providing back-drive protection for the source transmitter that it is connected to (which means it would provide a path for those currents to keep them out of the transmitter)?

The connection to the TPD12S016 is a single point for each of the TMDS signals and the functional circuit from the datasheet is attached.

Thanks,
Matthew

 

I'm not sure if this goes in the digital or analog section, so please forgive me if I chose poorly.

I have an FPGA that is an HDMI source. The design is working fine while everything is powered on. However, when I power down the FPGA board with the monitor still powered, the pull-up resistors in the TMDS sink (the monitor) back-drive into the FPGA and cause it to go into a quasi-powered state.

Apparently this is not uncommon, and there are buffer ICs and such. So I'm looking into a few options and I have found a chip that looks like what I need, the TPD12S016 (http://www.ti.com/lit/ds/symlink/tpd12s016.pdf)

The datasheet says it provides "Back-drive Protection on HDMI Connector Side Ports", "ESD protection", etc. What is unclear to me is if the back-drive "protection" is for the device itself, i.e. meaning the TPD12S016 will not provide a path for back-drive currents, or it the device is providing back-drive protection for the source transmitter that it is connected to (which means it would provide a path for those currents to keep them out of the transmitter)?

The connection to the TPD12S016 is a single point for each of the TMDS signals and the functional circuit from the datasheet is attached.

Thanks,
Matthew

 

Hi,
That's only a part of the functional diagram you've shown-the ESD bit.
The device does perform the function you need.
see the On semi datasheet for a better explanation.

 

Actually, the part I specified (TPD12S016) does not provide the back-drive protection.

However, I did find my answer. The TPD12S521 and TPD12S520 do provide back-drive protection for the ASIC/FPGA, as well as the NXP IP4786CZ32. The parameter used to indicate the back-drive protection is called Ibck or Iback-current depending on the datasheet.